Senior European lawmakers say they are shocked at reports that U.S. intelligence agents bugged EU offices on both sides of the Atlantic.

The president of the European Parliament said he was “deeply worried and shocked about the allegations of U.S. authorities spying on EU offices” made in a report published Sunday by German news weekly Der Spiegel.

Martin Schulz said if the reports were confirmed “it would be an extremely serious matter which will have a severe impact on EU-U.S. relations.”

Green Party leaders in the European Parliament, Rebecca Harms and Daniel Cohn-Bendit, called for an immediate investigation into reports published by Der Spiegel and suggested that further negotiations on a trans-Atlantic trade treaty be put on hold.

They also called for existing U.S.-EU agreements on the exchange of bank transfer and passenger record information to be canceled.